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I don't agree that this is a bug that should be fixed. It adds code that will likely never get called or needed (i.e. there has never been a request for this in the decade long history of desciptors and it seems like a made up requirement to me. 
I concur with Amrin's comment that this "is good enough" and Nick's comment that "it's just a matter of pattern of use'. I recommend that this be closed as "not-a-bug" and that we avoid gratuitous API expansion for what Larry states is likely "foolish consistency". 
If someone object to recommendation to close and really wants to push for this, I recommend making a business case for acceptance and then assigning this issue to Guido for a decision. This is his code and AFAICT he intentionally didn't go down a number of possible paths for descriptors simply because there weren't motivating use cases. To the extent that __call__ was omitted on some descriptors, I don't think it was an accident (most of this code was developed as the same time by the same person with deliberate differences between each of them). His write-ups for descriptors when they were introduced make no mention of an implied requirement for callability.
FWIW, issue 19072 isn't really related to this one. That issue is a feature request to support descriptor chainging and it isn't clear whether that should be supported or left as-in.